Differential data forming method, program, recording medium, and apparatus

ABSTRACT

Two new and old files are sequentially compared from heads of the files on a predetermined data unit basis. If a data coincidence is discriminated, transfer information showing a position and a data length of the old file is output. If a data dissidence is discriminated by the sequential comparison, the old file is searched in both forward and backward directions from a data position where the dissidence has been discriminated in the old file, thereby searching a portion which coincides with data of the new file. If the coincident portion can be searched, shift information up to the coincident portion on the old file is output. If the coincident portion cannot be searched, new data is added to transfer replacement information showing a length of data of the dissident portion of the old file at a position until the coincident portion can be searched, and the resultant transfer replacement information is output.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to a differential data forming method, a program, a recording medium, and an apparatus for forming differential data by comparing two new and old files. More particularly, the invention relates to a differential data forming method, a program, a recording medium, and an apparatus for forming differential data which is used in order to update an old file to a new file.

[0003] 2. Description of the Related Arts

[0004] If updating is necessary for version-up, backup, or the like of software on a computer or firmware of an apparatus, it is demanded to perform uploading and downloading at low costs even in a low-speed communication environment by using differential data formed by comparing two new and old files.

[0005] Hitherto, in the case of updating a file of a program, data, or the like to a new file, there are a method of replacing all new files and a method of providing differential data of only updating information of the files and updating. The updating method by the differential data has an advantage such that the updating can be performed by an information amount smaller than that in the case of the method of replacing all files, and is advantageous in terms of costs as the information amount is smaller in the case of transferring the updating information to locations where the old files exist. As a conventional method of forming the differential data, as shown in flowcharts of FIGS. 1A and 1B, there is a method (JP-A-4-163626) whereby two new and old files are compared from the heads, dissident portions are classified as updated portions into three categories “replacement”, “insertion”, and “deletion”, and values obtained after the updating according to

[0006] (1) the category of the updating, or

[0007] (2) the category of the “replacement” or “insertion”

[0008] are described as differential data. Processing steps in FIGS. 1A and 1B are as follows.

[0009] S1: The old file and new file are read out from a disk or the like.

[0010] S2: A data comparison target pointer is set to the head of the new file, and a data reference pointer I set to the head of the old file.

[0011] S3: A value indicated by the comparison target pointer is compared with a value shown by the data reference pointer.

[0012] S4: If a comparison result in step S3 indicates coincidence, step S5 follows. If they differ, step S7 follows.

[0013] S5: It is determined that the value shown by the comparison target pointer is a copy of the old file.

[0014] S6: A length of copy source is stored and step S14 follows.

[0015] S7: The data which coincides with the value shown by the data comparison target pointer is searched from the data existing behind the data reference pointer.

[0016] S8: As a result of the search, if the coincident data is found, step S11 follows. If the coincident data is not found, step S9 follows.

[0017] S9: It is determined that the comparison target data is the newly formed data.

[0018] S10: The data comparison target pointer is shifted to one-subsequent position and step S7 follows.

[0019] S11: It is determined that the coincident position was deviated due to the insertion of the new data or the deletion of the data of the old file.

[0020] S12: After a transfer code is written out, one of a replacement code, an insertion code, and a deletion code is written out in accordance with a shape of deviation.

[0021] S13: The data reference pointer is shifted by a distance corresponding to the deviation.

[0022] S14: Each of the data comparison target pointer and the data reference pointer is shifted to one-subsequent position.

[0023] S15: If the data comparison target pointer does not reach the end of the new file, the processing routine is returned to step S3. If it reached the end, the processing routine is finished.

[0024]FIGS. 2A and 2B show a replacing process in the conventional data forming method. An old file 200 in FIG. 2A is constructed by data A, B, and C. A new file 202 is constructed by data A, B′, and C. The data A and C denote coincident portions 204 and 208. The data B and B′ is a replacement portion 206. FIG. 2B shows a differential data file 210 formed by the flowcharts of FIGS. 1A and 1B. First, with respect to the coincident portion 204 of the data A, a transfer code 212 having a transfer code number and a copy source data length (a bytes) is written out. With respect to the replacement data 206 of the next data B and B′, a replacement code 214 having a replacement code number and a replacement data length (b bytes) is written out and differential data 216 of (B−B′) is added. Further, with respect to the coincident portion 208 of the data C, a transfer code 218 having a transfer code number and a copy source data length (c bytes) is written out.

[0025]FIGS. 3A and 3B show an inserting process in the conventional data forming method. The old file 200 in FIG. 3A is constructed by data A and B and the new file 202 is constructed by the data A and B and new data C inserted therebetween. The data A and B corresponds to the coincident portions 204 and 208 and the data C corresponds to the inserting portion 206. FIG. 3B shows the differential data file 210 formed by the flowcharts of FIGS. 1A and 1B. With respect to the coincident portions 204 and 208 of the data A and B, in a manner similar to FIG. 3B, the transfer codes 212 and 218 each having a transfer code number and a copy source data length are written out. With respect to an inserting portion 220 of the data C, an insertion code 222 having a transfer code number and an insertion data length (c bytes) is written out and insertion data 224 is added.

[0026]FIGS. 4A and 4B show a deleting process in the conventional data forming method. The old file 200 in FIG. 4A is constructed by data A, B, and C and the new file 202 is constructed by the data A and B and the data C is deleted. The data A and C corresponds to the coincident portions 204 and 208 and the data B corresponds to a deleting portion 226. FIG. 4B shows the differential data file 210 formed by the flowcharts of FIGS. 1A and 1B. With respect to the coincident portions 204 and 208 of the data A and C, in a manner similar to FIG. 3B, the transfer codes 212 and 218 each having a transfer code number and a copy source data length are written out. With respect to the deleting portion 226 of the data B, a deletion code 228 having a deletion code number and a deletion data length (b bytes) is written out.

[0027] However, such a conventional differential data forming method as mentioned above, since the updating information is expressed by three categories “replacement”, “insertion”, and “deletion” on the assumption that the correct coincident portions can be always found out when the coincident portions of the new and old files are searched, there are the following problems.

[0028]FIG. 5 shows an example of an inserting process. The old file 200 is constructed by data A and B. The new file 202 is constructed by the data A and B and also the data C inserted therebetween. With respect to the data A of the old file 200, the new file 202 has two coincident portions 204 and 230. However, according to the conventional differential data forming method, with respect to the second coincident portion 230, since it does not belong to all of the categories “replacement”, “insertion”, and “deletion”, there is a problem such that as for the insertion of the new data A, it is determined that all subsequent new and old files are dissident portions, they are written out only in the category “replacement”, and an amount of differential data increases.

[0029]FIG. 6 shows a case where a correspondence relation between the new and old files is wrong. It is now assumed that the old file is constructed by data A, B, C, and B and the new file is constructed by the data A, B, and C and the last data B is deleted. However, in the difference forming process, in the comparison between the data B of the old file 200 and the data B of the new file 202, if it is determined that the data B of the new file is erroneously recognized as data B′ and those data does not coincide, that is, if the updating portion is erroneously discriminated, a replacement code and new data B′ are erroneously formed as a category of “replacement”. In this case, even if the same data B as the data which was erroneously discriminated exists on the old file existing behind the position where the erroneous discrimination occurred, there is no room to utilize the data B. Upon updating of the old file, the data is erroneously rewritten to the data B′ which was erroneously discriminated. Further, in a program file, there is a case where by rewriting a specific program code, the same value repetitively appears as a differential value which is added to the replacement information. However, in the conventional differential data forming method, no consideration is made to such a point.

SUMMARY OF THE INVENTION

[0030] According to the invention, there are provided a differential data forming method, a program, a recording medium, and an apparatus, in which it is also possible to cope with patterns other than “replacement”, “insertion”, and “deletion” due to a comparison between new and old files, an amount of differential data is reduced, and even if a comparison discrimination about the new and old files is erroneously made, it can be corrected by subsequent processes, thereby raising reliability.

[0031] According to the invention, there is provided a differential data forming method comprising:

[0032] a comparing step wherein two new and old files are sequentially compared from heads of the files on a predetermined data unit basis;

[0033] a transfer information forming step wherein if a coincidence of the data is determined by the sequential comparison, transfer information (transfer code) showing a position and a data length of the old file is output;

[0034] a searching step wherein if a dissidence of the data is determined by the sequential comparison, the old file is searched in both forward and backward directions from a data position where the dissidence has been determined on the old file, thereby searching a portion which coincides with the data of the new file;

[0035] a shift information forming step wherein if the coincident portion can be searched in the searching step, shift information (shift code) up to the coincident portion on the old file is output; and

[0036] a replacement information forming step wherein if the coincident portion cannot be searched in the searching step, new data is added to transfer replacement information (transfer replacement code) showing a data length of the dissident portion of the old file at a position until the coincident portion can be searched and resultant transfer replacement information is output.

[0037] As mentioned above, according to the invention, if the dissidence of the data is determined by the sequential comparison between the new and old files, the old file is searched in both of the forward and backward directions, and the data in the old file which was once referred to can be again referred to. Beyond the conventional categories “replacement”, “insertion”, and “deletion”, it is also possible to cope with other patterns, the creation of redundant differential data is reduced, and a size of differential data is reduced. Even if the updating portion is erroneously made to correspond, in a subsequent difference extracting process, by again referring to the data in the old file which was once referred to, its influence is suppressed to the minimum, the creation of redundant differential data is reduced, and a size of differential data is reduced.

[0038] In the searching step, in the case where the portion in the old file which coincides with the data in the new file and the continuous coincident portions of a predetermined number (n) or more which are subsequent to the above coincident portion are searched, it is determined that the data coincides. This process is a coincidence discrimination corresponding to a case where the coincident portions are concentrated on specific portions of the new and old files. As mentioned above, according to the invention, there is executed the coincidence discrimination of two stages such that if one-byte data of the new file as a comparison target and one-byte data of the old file which was referred to coincide, further, only when subsequent (n) bytes or more coincide, the target portion is determined to be the coincident portion which is not updated, thereby correctly discriminating the coincident portion which is not updated and the dissident portion which is updated. At the same time, according to the coincidence discrimination of two stages, an opportunity of discriminating the dissident portion serving as an updating target is increased as much as possible, redundancy of the differential data is reduced by the replacing process regarding the dissident portion, and the size of differential data is reduced.

[0039] In the searching step, as another coincidence discrimination of two stages, it is also possible to construct in a manner such that if the portion in the old file which coincides with the data of the new file and the coincident portions of a predetermined number (y) or more of data distributed in a predetermined number (x) of data subsequent to such a coincident portion are searched, the data coincides. Such a discrimination is a coincidence discrimination in the case where the coincident portions are distributed in the new and old files.

[0040] In the shift information forming step, a shifting direction in which a forward position on the old file is set to a negative direction and a backward position on the old file is set to a positive direction and a shift length showing a length of data up to the coincident portion on the old file are output. In the searching step, if a structure of the file is that of a program file written by an n-bit code, the search is performed every other (n) bits in both forward and backward directions from the position of the data which was determined to be dissident in the old file, thereby searching the portion which coincides with the data in the new file. Thus, the coincident portion for the old file can be searched at a high speed.

[0041] In the replacement information forming step, when differential data between the old data and the new data coincides with differential data of replacement information formed in the past, the new data is not added but replacement information (transfer increase code) showing the same as a past differential pattern or updating pattern is output. For example, in the case where a specific program code has been changed or the like, new data of the same value is formed by the replacing process based on the dissidence discrimination of the new and old files each time the differential pattern having a value of the same difference appears. However, according to the invention, the new data of the same value is necessary only in the beginning and by making the new data unnecessary in the residual replacing process, the creation of redundant differential data is reduced, and a size of differential data is reduced. By increasing the opportunity of the replacing process due to the data dissidence as much as possible by the comparing process of the new and old files, the reduction of the differential data amount by the replacing process of the invention as mentioned above is further enhanced.

[0042] In the replacement information forming step, if the coincident portion cannot be searched in the searching step due to the insertion of the new data in the new file, the new data is added to the transfer replacement information showing the data length of the dissident portion of the old file at a position until the coincident portion can be searched and the resultant transfer replacement information is output. That is, the conventional inserting process is included in one form of the replacing process in the invention.

[0043] In the shift information forming step, if the coincident portion with the data of the new file cannot be searched in the searching step due to deletion of the data in the old file, shift information showing a shifting direction and the shift amount up to the backward coincident portion on the old file is formed. That is, the conventional deleting process is included in one form of the shifting process in the invention.

[0044] According to the invention, there is provided a program for forming differential data, wherein the program allows a computer to execute:

[0045] a comparing step wherein two new and old files are sequentially compared from heads of the files on a predetermined data unit basis;

[0046] a transfer information forming step wherein if a coincidence of the data is determined by the sequential comparison, transfer information showing a position and a data length of the old file is output;

[0047] a searching step wherein if a dissidence of the data is determined by the sequential comparison, the old file is searched in both forward and backward directions from a data position where the dissidence has been determined on the old file, thereby searching a portion which coincides with the data of the new file;

[0048] a shift information forming step wherein if the coincident portion can be searched in the searching step, shift information up to the coincident portion on the old file is output; and

[0049] a replacement information forming step wherein if the coincident portion cannot be searched in the searching step, new data is added to transfer replacement information showing a data length of the dissident portion of the old file at a position until the coincident portion can be searched and resultant transfer replacement information is output.

[0050] According to the invention, there is provided a computer-readable recording medium which stores a program for forming differential data, wherein the program stored in the recording medium allows a computer to execute:

[0051] a comparing step wherein two new and old files are sequentially compared from heads of the files on a predetermined data unit basis;

[0052] a transfer information forming step wherein if a coincidence of the data is determined by the sequential comparison, transfer information showing a position and a data length of the old file is output;

[0053] a searching step wherein if a dissidence of the data is determined by the sequential comparison, the old file is searched in both forward and backward directions from a data position where the dissidence has been determined on the old file, thereby searching a portion which coincides with the data of the new file;

[0054] a shift information forming step wherein if the coincident portion can be searched in the searching step, shift information up to the coincident portion on the old file is output; and

[0055] a replacement information forming step wherein if the coincident portion cannot be searched in the searching step, new data is added to transfer replacement information showing a data length of the dissident portion of the old file at a position until the coincident portion can be searched and resultant transfer replacement information is output.

[0056] According to the invention, there is provided a differential data forming apparatus comprising:

[0057] a data comparing unit which sequentially compares two new and old files from heads of the files on a predetermined data unit basis;

[0058] a transfer information forming unit which, if a coincidence of the data is determined by the data comparing unit, outputs transfer information showing a position and a data length of the old file;

[0059] a coincident portion search unit which, if a dissidence of the data is determined by the data comparing unit, searches the old file in both forward and backward directions from a data position where the dissidence has been determined on the old file, thereby searching a portion which coincides with the data of the new file;

[0060] a shift information forming unit which, if the coincident portion can be searched by the coincident portion search unit, outputs shift information up to the coincident portion on the old file; and

[0061] a replacement information forming unit which, if the coincident portion cannot be searched by the coincident portion search unit, adds new data to transfer replacement information showing a data length of the dissident portion of the old file at a position until the coincident portion can be searched and outputs resultant transfer replacement information.

[0062] Details of the program, recording medium, and differential data forming apparatus in the invention are fundamentally the same as those in the case of the differential data forming method.

[0063] The above and other objects, features, and advantages of the present invention will become more apparent from the following detailed description with reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0064]FIGS. 1A and 1B are flowcharts for a conventional differential data forming process;

[0065]FIGS. 2A and 2B are explanatory diagrams of a conventional replacing process;

[0066]FIGS. 3A and 3B are explanatory diagrams of a conventional inserting process;

[0067]FIGS. 4A and 4B are explanatory diagrams of a conventional deleting process;

[0068]FIG. 5 is an explanatory diagram of new and old file patterns which do not belong to conventional categories “replacement”, “insertion”, and “deletion”;

[0069]FIG. 6 is an explanatory diagram of new and old file patterns in which a correspondence relation of updating portions is wrong and which cannot be solved by a conventional method;

[0070]FIG. 7 is a functional block diagram in a construction of an apparatus of the invention;

[0071]FIGS. 8A to 8E are explanatory diagrams of differential control codes which are formed by the invention;

[0072]FIG. 9 is a schematic flowchart for a differential data forming process of the invention;

[0073]FIG. 10 is an explanatory diagram of new and old file patterns which can be processed by the invention;

[0074]FIG. 11 is an explanatory diagram of a differential data forming process by pointer control of the invention for new and old file patterns in FIG. 10 as targets;

[0075]FIG. 12 is an explanatory diagram of a differential data file formed by the process in FIG. 11;

[0076]FIG. 13 is an explanatory diagram of a coincident portion 2-stage discrimination in the invention;

[0077]FIG. 14 is an explanatory diagram of another coincident portion 2-stage discrimination in the invention;

[0078]FIG. 15 is an explanatory diagram of new and old file patterns in the case where an updating portion to be processed in the invention is erroneously discriminated;

[0079]FIG. 16 is an explanatory diagram of a differential data forming process by pointer control of the invention for new and old files in FIG. 15 as targets;

[0080]FIG. 17 is an explanatory diagram of a differential data file formed by the process in FIG. 16;

[0081]FIG. 18 is an explanatory diagram of new and old file patterns to which a replacing process is executed in the invention;

[0082]FIG. 19 is an explanatory diagram of the differential data forming process by the pointer control of the invention for new and old files in FIG. 18 as targets;

[0083]FIG. 20 is an explanatory diagram of a differential data file formed by the process in FIG. 19;

[0084]FIG. 21 is an explanatory diagram of the replacing process of the invention for differential data having the same value;

[0085]FIG. 22 is an explanatory diagram of new and old file patterns to which a shifting process of data deletion is executed in the invention;

[0086]FIG. 23 is an explanatory diagram of the differential data forming process by the pointer control of the invention for new and old files in FIG. 22 as targets;

[0087]FIG. 24 is an explanatory diagram of a differential data file formed by the process in FIG. 22;

[0088]FIG. 25 is an explanatory diagram of new and old file patterns to which a shifting process of data insertion is executed in the invention;

[0089]FIG. 26 is an explanatory diagram of the differential data forming process by the pointer control of the invention for new and old files in FIG. 25 as targets;

[0090]FIG. 27 is an explanatory diagram of a differential data file formed by the process in FIG. 26; and

[0091]FIGS. 28A to 28C are flowcharts for the differential data forming process according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0092]FIG. 7 is a block diagram of a functional construction of a differential data forming apparatus according to the invention. An old file 10 and a new file 12 are prepared as input files for the differential data forming apparatus. Both file data is read out by a data reading unit 14 and supplied to a differential data extracting unit 15. In the embodiment, for example, it is assumed that program files described by 32-bit codes (4-byte codes) are handled as an old file 10 and a new file 12. A data comparing unit 16, a transfer information forming unit 18, a coincident portion search unit 20, a shift information forming unit 22, and a replacement information forming unit 24 are provided for the differential data extracting unit 15. The data comparing unit 16 sequentially compares the two new and old files read out from the old file 10 and new file 12 by the data reading unit 14 from the heads of the files on a predetermined data unit basis, in the embodiment, on a one byte unit basis. If a coincidence of the new and old file data is determined by the data comparison of the byte unit by the data comparing unit 16, the transfer information forming unit 18 forms a transfer code indicative of a position and a data length of the coincident old file and outputs it.

[0093] The transfer code formed by the transfer information forming unit 18 has a format construction of FIG. 8A. A transfer code 36 is a code of 2 bytes, a code number “010” indicative of the transfer code 36 has been stored in head 3 bits of the first byte, and a transfer data length has been stored by using residual 5 bits of the first byte and 8 bits of the second byte.

[0094] Referring again to FIG. 7, if a data dissidence of the two new and old files which are compared on a byte unit basis by the data comparing unit 16 is determined, the coincident portion search unit 20 searches the old file in both forward and backward directions from the data position where the dissidence has been determined in the old file, thereby searching a portion which coincides with the data of the new file. In this case, if the old file is searched in the forward and backward directions on a byte unit basis, since it takes a time for a process, the data of the new file is compared with the data of the old file, for example, every other 4 bytes. If the coincident byte portion is found by searching the old file every other 4 bytes, it is determined that the coincident portions could be searched by coincidence discrimination of two stages which satisfy one of the following conditions.

[0095] (1) If the coincident portions of a length of a predetermined number (n) of bytes or more, for example, n=16 bytes or more subsequent to the portion in the old file which coincides with the 1 byte data of the new file have continuously been searched, it is determined that the data coincides.

[0096] (2) If the coincident portions of another predetermined number (y) of bytes or more, for example, y=32 bytes or more distributed in a predetermined number (x) of data or more, for example, x=64 bytes subsequent to the portion in the old file which coincides with the 1-byte data of the new file have been searched, it is determined that the data coincides.

[0097] The reasons why the old file is searched in the forward and backward directions from the dissident position and after the coincidence of the 1-byte portion is obtained, the coincident portion is discriminated at two stages on the basis of one of the conditions (1) and (2) as mentioned above are to certainly execute the coincidence discrimination in the differential data extracting process of the new and old files and to reduce a data amount by decreasing redundancy of the differential data by increasing an opportunity of a replacing process as much as possible in the differential data extracting process. If the coincident portion could be searched by searching the old file in the forward and backward directions from the dissident position of the old file by the coincident portion search unit 20, the shift information forming unit 22 forms a shift code indicative of shift information in a range from the dissident portion to the coincident portion on the old file and outputs it. The shift code has a shifting direction in which the forward position on the old file is set to the negative direction and the backward position on the old file is set to the positive direction and a shift length showing a length of data in a range from the dissident portion to the coincident portion on the old file.

[0098] Specifically speaking, a negative shift code 42 in FIG. 8D or a positive shift code 44 in FIG. 8E is formed and output. Each of the negative shift code 42 and the positive shift code 44 is code information of 2 bytes in a manner similar to the transfer code 36 in FIG. 8A. With respect to head 2 bits of the first byte, in the negative shift code 42, a code number “10” has been stored and, after that, the shift length on the old file has been stored by using 6 bits of the first byte and 8 bits of the second byte. In a manner similar to the above, in the positive shift code 44 in FIG. 8E, a code number “11” indicative of a positive control code has been stored in head 2 bits of the first byte and, after that, the shift length has been stored by using residual 6 bits of the first byte and 8 bits of the second byte.

[0099] Referring again to FIG. 7, when the coincident portion cannot be searched by the coincident portion search unit 20, the replacement information forming unit 24 adds new data in the dissident portion to a transfer replacement code showing the data length of the dissident portion of the old file at a position until the coincident portion can be searched and outputs the resultant transfer replacement code. The transfer replacement code which is formed and output by the replacement information forming unit 24 is a control code of 2 bytes as shown in FIG. 8B, a code number “00” indicative of a transfer replacement code 38 has been stored in 2 bits of the first byte, a replacement data length has been stored in 6 bits subsequent to the code number, and a transfer data length (transfer data length at a position until the replacement occurs) has been stored in 8 bits of the second byte.

[0100] When replacement information is formed, the replacement information forming unit 24 of the invention discriminates whether replacement information having a difference of the same value has been formed by the differential data extracting process so far or not. If the replacement information having the difference of the same value has been formed, the replacement information forming unit 24 does not form new data but forms a transfer increase code 40 in FIG. 8C as replacement information indicative of the existence of the existing differential information and outputs it. The transfer increase code 40 is a control code of 2 bytes, a code number “011” indicative of the transfer increase code has been stored in head 3 bits of the first byte, a transfer data length has been stored by using 5 bits subsequent to the code number and 8 bits of the second byte. That is, if the value of the difference of the replacing process is equal to the first value which did not exist in the past, the replacement information forming unit 24 of the invention generates the transfer replacement code 38 in FIG. 8B, adds new data thereto, and outputs the resultant transfer replacement code. In the case of the second and subsequent times in which the value of the difference has the same value in the past, the transfer increase code 40 in FIG. 8C is formed and output. In this case, there is no need to add the new data. Therefore, in the case where a plurality of differential patterns having the same difference appear, it is sufficient to add the new data only once and there is no need to add the new data after that. Thus, the redundancy of the differential data can be reduced and an amount of differential data can be decreased.

[0101] The control code in each of the transfer information, shift information, and replacement information formed by the differential data extracting unit 15 in FIG. 7 is written out as a control code 30 by a control code writing unit 26 and written into a differential data file 35 by a differential data writing unit 34. The new data written in association of the creation of the transfer replacement code 38 in FIG. 8B in the replacement information forming unit 24, that is, the updating data is written out as updating data 32 by an updating data writing unit 28 and written into the differential data file 35 via the differential data writing unit 34.

[0102]FIG. 9 is a schematic flowchart for a differential data forming process according to the invention corresponding to the differential data processing apparatus of FIG. 7. In step S1, the new and old files are read and compared, for example, on a byte unit basis. If a coincidence of the 1-byte data of the new and old files is determined in step S2, transfer information (transfer code) is formed in step S3. If the data coincidence is not obtained in step S2, that is, in the case of a dissidence, portions before and after the dissident portion in the old file corresponding to the 1-byte data in the new file are searched, thereby searching the coincident portion in step S5. As for the coincident portion, after the coincidence is obtained by searching the portions before and after the dissident portion in the old file, when the continuous coincidence of n=16 bytes or more subsequent to the coincident 1-byte data or the coincidence of 32 bytes or more in x=64 bytes subsequent to one byte is obtained, it is determined that the data coincides. If the coincident portion is obtained with respect to the search result about the coincident portion in step S6, shift information (positive shift code or negative shift code) is formed in step S7. If there is no coincident portion, a replacement information forming process is executed in step S8. In the case where the value of the difference is equal to the value obtained in the beginning, the replacement information forming process generates the transfer replacement code 38 in FIG. 8B, adds new data obtained after the updating thereto, and outputs the resultant transfer replacement code. In the replacement of the second and subsequent times in which the value of the difference has the same value, the transfer increase code 40 in FIG. 8C is formed and output. Thus, there is no need to add the new data. Such processes are repeated up to a file end position in step S4.

[0103]FIG. 10 shows an example of new and old file patterns which cannot be processed by the conventional method that is peculiar to the differential data forming process of the invention. The new and old file patterns are the data A and B in the old file 10. They are updated to the data A, A, and B in the new file 12. In the new file 12, a coincident portion 52 of the data A is newly added with respect to a coincident portion 50 of the data A and a coincident portion 54 of the data B is finally added.

[0104]FIG. 11 shows a specific processing procedure of the differential data forming process according to the invention for the new and old file patterns in FIG. 10 as targets. In the differential data forming process according to the invention, a data comparison target pointer P is set into the new file 12. In response to it, a data reference pointer Q is set into the old file 10. The differential data forming process is executed by the control of the positions of the pointers P and Q. In the following description, the data comparison target pointer P and the data reference pointer Q are simply referred to as pointers and numbers are added to those pointers, like (P1, P2, P3) or (Q1, Q2, Q3), in control order of the pointers. Further, data lengths of the data A, B, and C are assumed to be (a) bytes, (b) bytes, and (c) bytes, respectively.

[0105] In FIG. 11, first, the pointers P1 and Q1 are set to the heads of the new file 12 and the old file 10, respectively, and the 1-byte data shown by a broken line is compared. In this case, since the data A is the coincident portion 50, the 1-byte data coincides as a result of the first 1-byte comparison. Therefore, when the coincidence is obtained, the pointers P1 and Q1 are shifted to the next positions deviated by one byte, and the 1-byte data is compared. Thus, with respect to the data A in the new file 12 and the old file 10, the result of the byte coincidence is obtained up to P2 and Q2. Subsequently, with respect to the new file 12 and the old file 10, the pointers are shifted to the pointers P3 and Q3 and the next one byte is compared. In this case, it is the head byte of each of the data A and B and the 1-byte data does not coincide. If the dissidence is obtained by the comparison of the 1-byte data as mentioned above, in the invention, the pointer is shifted to the positions before and after the pointer Q3 as a dissident position in the old file 10, and the coincident portion with the 1-byte data of the pointer P3 in the new file 12 is searched. In the search of the coincident portions at the positions before and after the pointer Q3 at the dissident position in the old file 10, for example, the 1-byte data of the old file 10 is extracted every other 4 bytes and compared. By this search, the head one byte in the forward data A in the old file 10 coincides with one byte of the pointer P3 in the new file 12. If the coincident portion is discriminated from the old file 10 by the search of the coincident portions before and after the dissident position, the pointer Q3 is shifted to a pointer Q3′ of the coincident portion. The comparison is sequentially performed on a byte unit basis from the 1-byte data of the pointer P3 of the new file 12 and one byte of Q3′ of the old file shifted by the search. In this case, since both data is the data A, the data coincidence of the byte unit is obtained up to the pointers P4 and Q4. Subsequently, when the pointer is shifted to P5 and Q5 and the head bytes of the data B are compared, also in this case, the data coincidence is obtained and this data coincidence continues up to the last pointers P6 and Q6.

[0106] By the extracting process of the differential data by the control of the pointer in FIG. 11 as mentioned above, a transfer code 56, a negative shift code 58, and a transfer code 60 as shown in the differential data file 35 in FIG. 12 are formed and output. First, in the head data A in the new and old files in FIG. 11, the transfer code 56 in which code contents have (a) bytes as a data length of the data A is formed. Subsequently, the negative shift code 58 showing the shift from the pointer Q3 to Q3′ at the time when the coincidence with the head byte of the data A is obtained by the search of the portions before and after the dissident portion in the old file 10 due to the dissident portion of the 1-byte data of the pointers P3 and Q3 is formed. Since the negative shift code 58 indicates the shift in the negative direction in which the pointer Q3 shifts to the forward pointer Q3′, the negative shift code 58 is formed and −a bytes showing a deviation amount of the pointer are stored as a shift length. Lastly, the transfer code 60 indicative of the coincidence between the second data A and the last data B in the new file 12 and the data A and B in the old file 10 is formed and output. In this case, the transfer data length is equal to (a+b) bytes obtained by adding byte lengths (a) and (b) of data (a) and (b).

[0107]FIG. 13 shows a specific example of a coincidence discrimination at the second stage which is subsequently executed in the case where the 1-byte data does not coincide at the pointers P3 and Q3 in FIG. 11, the old file 10 is searched in the forward and backward directions, and the 1-byte data coincides with the head 1-byte data of the forward data A. That is, FIG. 13 corresponds to the case where since 1-byte data 62 of the new file 12 and 1 byte data 64 of the old file 10 do not coincide, the old file is searched backward, and the coincidence with 1-byte data 66 is searched. In this case, as a data portion 70 subsequent to the searched 1-byte data 66, if it coincides with a data portion 68 of the new file 12 by n=16 bytes or more, it is determined that the coincident portions could be searched.

[0108]FIG. 14 is an explanatory diagram of another coincident portion discriminating process of two stages in the coincidence search. In this case, when a coincidence with the 1-byte data 66 is determined by searching the backward portion of the 1-byte data 62 of the new file 12, if the portions of y=32 bytes or more in x=64 bytes subsequent thereto coincide, that is, when the total number of bytes of coincident portions of data portions 72-1 to 72-5 and 74-1 to 74-5 in the new and old files 12 and 10 subsequent to the coincident 1-byte data 62 and 66 is equal to y=32 bytes or more, it is determined that the coincident portions could be searched. As mentioned above, when one of the coincidence conditions in FIG. 13 or 14 is satisfied, it is determined that a deviation occurred between the coincident positions in the new file 12 and the old file 10, thereby generating the negative shift code 42 in FIG. 8D or the positive shift code 44 in FIG. 8E in accordance with the direction of the deviation. By the generation of the negative shift code 42 or the positive shift code 44 indicative of the occurrence of the deviation, a process which is executed after the pointer is shifted by the deviation amount on the old file 10 becomes the differential data extracting process by the comparison of the byte unit from the pointer position which was deviated again.

[0109]FIG. 15 is an explanatory diagram of new and old file patterns which can be processed in the invention in the case where an updating portion is erroneously discriminated. The old file 10 is constructed by data A, B, C, and B. On the other hand, the new file 12 obtained after the updating is constructed by data A, B, and C. If the differential data forming process is normally executed, since all of the data A, B, and C is the coincident portions, it is sufficient to form and output a transfer code of (a+b+c) bytes corresponding to a transfer data length. However, it is now assumed that an erroneous discrimination was made in the process of the second data B and the data of the new file 12 was erroneously discriminated to be B′ for the data B of the old file 10. With respect to such an erroneous discrimination in which the data B was erroneously discriminated to be the data B′ as mentioned above, according to the conventional method, since the data differs, differential data is formed by the replacing process, so that the result of the erroneous discrimination is inherited as wrong data to the subsequent updating of the old file 10. According to the invention, however, if the data B was erroneously discriminated as data B′, since the data does not coincide, the old file 10 is searched in the forward and backward directions of the data B serving as a dissident portion in the old file 10. In this case, the data B which coincides by the backward search is searched as a coincident portion, the pointer is shifted to the head of the data B behind the old file 10, and the differential data extracting process is executed, so that a transfer code to transfer the data B at the end of the old file 10 is formed. Thus, data of a portion 78 which was erroneously discriminated first is updated to correct data. The pointer shifted from the erroneously discriminated portion 78 to the data B behind the old file 10 is contrarily returned to the head of the data C by a pointer shift 82 in the negative direction after completion of the differential data extracting process of the data B, and a transfer code in which the data C is set to a coincident portion 80 is formed and output.

[0110]FIG. 16 is an explanatory diagram according to pointer control of a differential data forming process of the invention for new and old files in the case where the erroneously discriminated portion 78 in FIG. 15 is included. Processes of the portion between the pointers P1 and P2 and between the pointers Q1 and Q2 corresponding to the data A in the new and old files 12 and 10 are substantially the same as those in the case of FIG. 6 (the transfer code is generated). When head one byte of the data B′ is compared with the data B of the old file 10 of the pointer Q, they are erroneously discriminated to be dissident due to the shift of the pointer P3. Due to such an erroneous discrimination, according to the invention, the search is performed in the forward and backward directions for the pointer Q3 of the dissident portion. In this case, since the erroneously discriminated data B′ of the old file 10 is inherently correctly the data B, the data coincides by the search of head one byte of the last data B of the old file 10. At this time, assuming that the coincidence condition at the second stage in FIG. 13 or 14 is satisfied, the portion which coincides with the data B is discriminated, the pointer Q3 of the old file 10 is shifted to Q3′, and in association with it, a positive shift code 84 shown in the differential data file 35 in FIG. 17 in which +(c+b) bytes as a deviation from the pointer Q3 have been stored is generated. Subsequently, a coincidence of the data B is determined due to the shift of the pointers P3 to P4 of the new file 12 and the shifted pointers Q3′ to Q4 of the old file 10, and a transfer code 86 of (b) bytes of the transfer data length in FIG. 17 is formed. Subsequently, even when the pointer P5 of the new file 12 is compared with the end pointer Q5 of the old file 10, they do not coincide. Therefore, since the data exists only in the forward and backward directions of the pointer Q5, in this case, only in the forward direction, a coincidence with the head byte of the data C is discriminated by searching the old file in the forward direction. Owing to the coincidence of the 1-byte data, when the coincidence conditions of FIG. 13 or 14 are subsequently obtained, the data is determined to be the coincident portion and the pointer Q5 is shifted to Q5′. To show such a shift of the pointer, a negative shift code 88 in FIG. 17 in which a shift length of −(c+b) bytes has been stored is generated. By the coincidence of the data C due to the shift of the pointers P5 to P6 of the new file 12 and the shifted pointers Q5′ to Q6 of the old file 10, a transfer code 90 of (c) bytes as a transfer data length in FIG. 17 is generated. As mentioned above, in the differential data forming process of the invention, it is possible to properly cope with the new and old file patterns which cannot be coped by the categories “replacement”, “deletion”, and “insertion” in the conventional differential data forming method. Even if the replacement position was erroneously discriminated, by the subsequent processes, by again referring to the portion of the old file which was once referred to, the differential data of the erroneously discriminated portion can be corrected.

[0111]FIG. 18 shows new and old file patterns having an updating portion. In the new and old file patterns, the old file 10 is constructed by data A, B, and C and the new file 12 is constructed by data A, B′, and C. There are the coincident portions of the data A and C and the portions of the data B and B′ become replacement data 96.

[0112]FIG. 19 shows a specific example by the pointer control of the differential data forming process of the invention for the new and old file patterns in FIG. 18. In FIG. 19, in the head data A of the new and old files, a coincidence of the data A is discriminated by control of the pointers P1 to P2 and the pointers Q1 to Q2. Subsequently, head one byte of each of the data B and B′ is compared due to the shift to the pointer P3 of the new file 12 and the pointer Q3 of the old file 10. In this case, the data does not coincide due to the updating. Due to the dissidence of the 1-byte data, even if the old file is searched in the forward and backward directions of the old file 10, the coincident portion cannot be obtained. Therefore, the pointers P3 and Q3 are shifted backward one byte by one and this process is repeated up to the pointers P4 and Q4. Further, when the pointers are shifted to the pointers P5 and Q5, head one byte of the next data C is compared and the data is determined to be the coincident portion. At the same time, since the coincidence condition of the second stage of FIG. 13 or 14 is satisfied, the data is determined to be the coincident portion. Therefore, with respect to the data B and B′ serving as replacement portion at this point of time, a transfer replacement code 102 of (c) bytes as a replacement data length and (a) bytes as a transfer data length in FIG. 20 is generated. A value (B−B′) of a difference at this time is obtained. Since this difference value (B−B′) is a value which does not coincide with a value of the differential data of the past replacement code and appears for the first time, the transfer replacement code 102 is formed, new data 104 having a value of B′ is added to the code 102, and the resultant code is output. In FIG. 19, the coincident portion of the data C is discriminated by the shift of the pointers P5 to P6 in the new file 12 and the shift of the pointers Q5 to Q6 in the old file 10 synchronized therewith. A transfer code 106 of (c) bytes as a transfer data length in FIG. 20 is formed.

[0113]FIG. 21 is an explanatory diagram of a process in the case where a value of the same difference is repeated as a differential pattern of a replacement portion in the replacing process having the replacement data 96 as shown in FIG. 18. In the old file 10 and the new file 12, a byte code of 4 bits is expressed by a hexadecimal numerical value. When the new and old files are compared, dissident portions 118, 120, 122, and 124 exist between coincident portions 108, 110, 112, 114, and 116, respectively. In the dissident portions 118 to 124, each difference between the 2-byte data of the old file 10 and the 2 byte data of the new file 12 is equal to the same hexadecimal value “11”. In such a case, in the differential data forming process of the invention, since the difference of the data bytes in the head dissident portion 118 is equal to the value obtained for the first time, the transfer replacement code 38 in FIG. 8B is generated and new data “16” is added thereto. On the other hand, with respect to the second and subsequent dissident portions 120, 122, and 124, since the differences of the data bytes are equal to the same hexadecimal value “11”, in this case, the transfer increase code 40 in FIG. 8C is generated and new data is not added. Thus, redundancy of the differential data which is formed by the replacing process can be reduced and a differential data amount can be largely decreased. In this case, on a reconstructing side of the differential data, the difference “11” between the new data “16” added to the transfer replacement code 38 and the old data is obtained. When the transfer increase code 40 is received after that, the new data can be reconstructed by adding the difference “11” to the corresponding old data.

[0114]FIG. 22 is an explanatory diagram of new and old file patterns to which a shifting process of data deletion is executed by the invention. In the new and old file patterns, by setting the data B among data A, B, and C of the old file 10 to deletion data 130, data A and C of the new file 12 is obtained. Portions corresponding to the data A and C in the new file 12 become coincident portions 126 and 128.

[0115]FIG. 23 shows the differential data forming process by the pointer control for new and old file patterns in FIG. 22. In this case, a dissidence with the 1-byte data of the pointer Q3 of the old file 10, that is, with the head byte of data C is discriminated at the position of the pointer P3 of the new file 12. By searching the old file in the forward and backward directions of the dissident portion, a data coincidence is obtained at the head byte of the data B which is deviated backward by +c bytes. Therefore, the pointer Q3 of the old file 10 is shifted to the pointer Q3′. By the shift to the pointer Q3′, a positive shift code 134 of +c bytes as a second shift length in the differential data file 35 in FIG. 24 is generated. The control code in the data A and B of the preceding coincident portions are transfer codes 132 and 136.

[0116]FIG. 25 is an explanatory diagram of new and old file patterns to which a shifting process of data insertion is executed in the invention. In this case, data C is inserted between data A and B of the old file 10 as shown in the new file 12, thereby forming insertion data 140.

[0117]FIG. 26 shows the differential data forming process by the pointer control of the invention for new and old file patterns in FIG. 25. In this case, head one byte of each of the data C and B does not coincide at the positions of the pointer P3 of the new file 12 and the pointer Q3 of the old file 10, and even if the old file is searched in the forward and backward directions of the dissident portion in the old file 10, the coincident portion is not obtained. Therefore, the pointers are sequentially shifted backward with respect to the new file 12 and the old file 10. When they are shifted to the pointers P4 and Q4, the 1-byte data does not coincide. Subsequently, when they are shifted to the pointers P5 and Q5, the 1-byte data does not coincide. In association with it, by searching the old file in the forward and backward directions of the dissident portion on the old file 10, the coincident portion with the head one byte of the data B is discriminated. By such a discrimination of the coincident portion, the data C of the pointers P3 to P4 in the new file 12 can be determined to be the new data, that is, the data serving as an inserting portion. Therefore, in the differential data file 35 in FIG. 27, a transfer replacement code 146 is generated by the replacing process. New data 148 having the value of C is added to the transfer replacement code 146 and the resultant code is output. Subsequently, in FIG. 26, a negative shift code 150 showing that the pointer Q5 has been shifted in the negative direction as a forward direction by −c bytes in the old file 10 and becomes the pointer Q5′ is formed and output. Lastly, the coincident portion of the data B is discriminated by the synchronous shift of the pointers P5 to P6 and the pointers Q5′ to Q6′ and a transfer code 152 in FIG. 27 is formed and output.

[0118]FIGS. 28A to 28C are flowcharts to realize a program for specifically realizing the differential data forming process according to the invention shown in FIGS. 10 to 27. First, in step S1, the old file and the new file are read out. In next step S2, the data comparison target pointer P and the data reference pointer Q are set to the heads of the files, respectively. In step S3, values of the data comparison target pointer P and the data reference pointer Q are compared. In step S4, if the compared data, that is, the 1-byte data has the same value, step S5 follows and this 1-byte data is determined to be a copy of the data of the old file. In step S6, a position and a length of a copy source are stored. In next step S7, each of the data comparison target pointer P and the data reference pointer Q is shifted backward by one byte. In step S8, if the data comparison target pointer P is not the end of the new file, the processing routine is returned to step S3 and similar processes are repeated. In step S8, if the data comparison target pointer P is the end of the new file, step S22 follows. If a non-processed copy source has been stored, the transfer code is written out in step S23. Thereafter, the series of processes is finished. If the compared data does not coincide in step S4, the processing routine advances to step S9 in FIG. 28B. In step S9, positions where the value coincides with the data of the new file is searched from the old file every other 4 bytes at positions before and after the data comparison position. If the coincident portion cannot be found in step S10, it is determined in step S11 that the compared data is the newly formed data. In step S12, the data comparison target pointer P is shifted backward by one byte. If the insertion data exists in the new file, the processes in steps S9 to S12 are repeated up to the last 1-byte data of the insertion data. If the coincident portion is found in step S10, step S13 follows. As shown in FIG. 8, whether the data of (n) bytes behind the coincident portion continuously coincides or not is discriminated. If this condition is not satisfied, step S14 follows and whether the data of (y) bytes in the (x) bytes behind the coincident portion coincides as shown in FIG. 9 or not is discriminated. If one of the conditions in steps S13 and S14 is satisfied, step S15 follows and it is determined that a deviation of the coincident portion has occurred. Subsequently, in step S16, whether the deviation of the data comparison target pointer P and that of the data reference pointer Q are the same or not is discriminated. If they differ, since this means that the data reference pointer Q has been deviated, in step S17, the transfer code based on the information stored in step S6 is written out and the shift code indicative of the shift of the pointer is written out. Upon writing of the shift code, if the shift is the shift in the negative direction as a forward direction, a negative shift code is generated, and if it is the shift in the positive direction as a backward direction, a positive shift code is generated. In step S18, the data reference pointer Q is shifted by a distance corresponding to the deviation. If the deviation of the data comparison target pointer P and that of the data reference pointer Q are the same in step S16, it is determined that the process is the replacing process. Step S19 follows. In step S19, whether the difference from the data of the old file coincides with the previous one or not is discriminated. If the differential data does not coincide with the previous one, step S21 follows. The transfer code is written out on the basis of the information stored in step S6, thereafter, the transfer replacement code indicative of the replacement is written out, and further, the value of the difference from the data of the old file is stored. If the difference from the data of the old file coincides with the previous one in step S19, step S20 follows. The transfer code according to the contents stored in step S6 is written out and, thereafter, the transfer increase code which does not need to add the new data is written out. The above processes are repeated until the data comparison target pointer P reaches the end of the new file in step S8 in FIG. 23.

[0119] An embodiment of a computer-readable recording medium in which a program for realizing the differential data forming process of the invention has been stored will now be described. A computer system which executes the program for performing the differential data forming process of the invention comprises a CPU, an RAM, an ROM, a hard disk drive, a CD-ROM drive, an FD drive, a keyboard, a mouse, a display, an input/output interface, an LAN interface, a modem, and the like. The differential data forming program of the invention is stored into a recording medium, for example, a portable memory medium such as CD-ROM, floppy disk (R), DVD disk, magnetooptic disk, IC card, or the like, a database connected via a line by using a modem or an LAN interface, or a database of another computer system, installed into a computer which realizes the invention, and thereafter, executed.

[0120] As described above, according to the invention, if the dissidence is discriminated due to the sequential comparison of the new and old files, the old file is searched in both of the forward and backward directions of the old file and the data in the old file which was once referred to can be again referred to. Thus, it is also possible to cope with other patterns exceeding the conventional categories “replacement”, “insertion”, and “deletion”, the creation of the redundant differential data can be reduced, and the size of differential data can be decreased.

[0121] Owing to the sequential comparison of the new and old files, even if the process to allow the updating portion to correspond was erroneously performed, in the subsequent processes, by again referring to the data in the old file which was once referred to, the erroneously formed portion can be corrected, influence by the error of the correspondence process is suppressed to the minimum, and the reliability of the updating by the differential data can be improved.

[0122] In the updating process of the invention, if a plurality of patterns having the same difference are formed, although the new data obtained after the updating is necessary for the first time, by forming the replacement information showing the use of the past pattern with respect to the second and subsequent patterns, the addition of the new data becomes unnecessary. Even if the replacing process increases, the redundancy of the differential data can be reduced and the size of differential data can be decreased.

[0123] In the invention, in the case where the dissidence of, for example, the byte data of the new and old files is determined, if the coincidence of the byte data is obtained by searching the old file in the forward and backward directions of the dissident portion in the old file, when the coincidence of the data of a predetermined number of bytes or more subsequent to it is obtained or the coincidence of the data of another predetermined number of bytes or more among subsequent predetermined bytes is obtained, it is determined that the relevant portion is the coincident portion. The shift information indicative of the deviation of the data is output. The shift information indicative of the control position on the old file, that is, the deviation of the pointer is certainly generated. If the coincident portions of a certain number cannot be obtained in the lump, by executing the replacing process, an opportunity of forming the replacement information is increased. If the opportunity of forming the replacement information is increased, the replacement information which does not need the addition of the new data at the second and subsequent times can be formed with respect to the same pattern. Thus, the redundancy of the differential data amount can be reduced as a whole and the size of differential data can be decreased.

[0124] The invention is not limited to the foregoing embodiments and incorporates proper modifications so long as they can accomplish the objects and advantages of the invention. The invention is not limited by the numerical values shown in the foregoing embodiment. 

What is claimed is:
 1. A differential data forming method comprising: a comparing step wherein two new and old files are sequentially compared from heads of the files on a predetermined data unit basis; a transfer information forming step wherein if a coincidence of the data is determined by said sequential comparison, transfer information showing a position and a data length of the old file is output; a searching step wherein if a dissidence of the data is determined by said sequential comparison, the old file is searched in both forward and backward directions from a data position where the dissidence has been determined on the old file, thereby searching a portion which coincides with the data of the new file; a shift information forming step wherein if the coincident portion can be searched in said searching step, shift information up to the coincident portion on the old file is output; and a replacement information forming step wherein if the coincident portion cannot be searched in said searching step, new data is added to transfer replacement information showing a data length of the dissident portion of the old file at a position until the coincident portion can be searched and resultant transfer replacement information is output.
 2. A method according to claim 1, wherein in said searching step, when a portion of the old file which coincides with the data of the new file and continuous coincident portions of a predetermined number (n) or more of data subsequent to said coincident portion are searched, it is determined that the data coincides.
 3. A method according to claim 1, wherein in said searching step, when a portion of the old file which coincides with the data of the new file and coincident portions of a predetermined number (y) or more of data distributed among a predetermined number (x) of data subsequent to said coincident portion are searched, it is determined that the data coincides.
 4. A method according to claim 1, wherein in said shift information forming step, a shifting direction in which a forward position on said old file is set to a negative direction and a backward position on said old file is set to a positive direction and a shift length showing a length of data up to the coincident portion on the old file are output as said shift information.
 5. A method according to claim 1, wherein in said searching step, if a structure of the file is that of a program file written by an n-bit code, the search is performed every other (n) bits in both forward and backward directions from the position of the data which was determined to be dissident in the old file, thereby searching the portion which coincides with the data in the new file.
 6. A method according to claim 1, wherein in said replacement information forming step, when differential data between the old data and the new data coincides with differential data of replacement information formed in the past, the new data is not added but transfer replacement information showing the same as a past differential pattern or updating pattern is output.
 7. A method according to claim 1, wherein in said replacement information forming step, if the coincident portion cannot be searched in said searching step due to the insertion of the new data in the new file, said new data is added to the transfer replacement information showing the data length of the dissident portion of the old file at a position until the coincident portion can be searched and the resultant transfer replacement information is output.
 8. A method according to claim 1, wherein in said shift information forming step, if the coincident portion with the data of the new file cannot be searched in said searching step due to deletion of the data in the old file, shift information showing a shifting direction and the shift amount up to the backward coincident portion on the old file is formed.
 9. A program for forming differential data, wherein said program allows a computer to execute: a comparing step wherein two new and old files are sequentially compared from heads of the files on a predetermined data unit basis; a transfer information forming step wherein if a coincidence of the data is determined by said sequential comparison, transfer information showing a position and a data length of the old file is output; a searching step wherein if a dissidence of the data is determined by said sequential comparison, the old file is searched in both forward and backward directions from a data position where the dissidence has been determined on the old file, thereby searching a portion which coincides with the data of the new file; a shift information forming step wherein if the coincident portion can be searched in said searching step, shift information up to the coincident portion on the old file is output; and a replacement information forming step wherein if the coincident portion cannot be searched in said searching step, new data is added to transfer replacement information showing a data length of the dissident portion of the old file at a position until the coincident portion can be searched and resultant transfer replacement information is output.
 10. A program according to claim 9, wherein in said searching step, when a portion of the old file which coincides with the data of the new file and continuous coincident portions of a predetermined number (n) or more of data subsequent to said coincident portion are searched, it is determined that the data coincides.
 11. A program according to claim 9, wherein in said searching step, when a portion of the old file which coincides with the data of the new file and coincident portions of a predetermined number (y) or more of data distributed among a predetermined number (x) of data subsequent to said coincident portion are searched, it is determined that the data coincides.
 12. A program according to claim 9, wherein in said shift information forming step, a shifting direction in which a forward position on said old file is set to a negative direction and a backward position on said old file is set to a positive direction and a shift length showing a length of data up to the coincident portion on the old file are output as said shift information.
 13. A program according to claim 9, wherein in said searching step, if a structure of the file is that of a program file written by an n-bit code, the search is performed every other (n) bits in both forward and backward directions from the position of the data which was determined to be dissident in the old file, thereby searching the portion which coincides with the data in the new file.
 14. A program according to claim 9, wherein in said replacement information forming step, when differential data between the old data and the new data coincides with differential data of replacement information formed in the past, the new data is not added but transfer replacement information showing the same as a past differential pattern or updating pattern is output.
 15. A program according to claim 9, wherein in said replacement information forming step, if the coincident portion cannot be searched in said searching step due to the insertion of the new data in the new file, said new data is added to the transfer replacement information showing the data length of the dissident portion of the old file at a position until the coincident portion can be searched and the resultant transfer replacement information is output.
 16. A program according to claim 9, wherein in said shift information forming step, if the coincident portion with the data of the new file cannot be searched in said searching step due to deletion of the data in the old file, shift information showing a shifting direction and the shift amount up to the backward coincident portion on the old file is formed.
 17. A computer-readable recording medium which stores a program for forming differential data, wherein said program allows a computer to execute: a comparing step wherein two new and old files are sequentially compared from heads of the files on a predetermined data unit basis; a transfer information forming step wherein if a coincidence of the data is determined by said sequential comparison, transfer information showing a position and a data length of the old file is output; a searching step wherein if a dissidence of the data is determined by said sequential comparison, the old file is searched in both forward and backward directions from a data position where the dissidence has been determined on the old file, thereby searching a portion which coincides with the data of the new file;. a shift information forming step wherein if the coincident portion can be searched in said searching step, shift information up to the coincident portion on the old file is output; and a replacement information forming step wherein if the coincident portion cannot be searched in said searching step, new data is added to transfer replacement information showing a data length of the dissident portion of the old file at a position until the coincident portion can be searched and resultant transfer replacement information is output.
 18. A differential data forming apparatus comprising: a data comparing unit which sequentially compares two new and old files from heads of the files on a predetermined data unit basis; a transfer information forming unit which, if a coincidence of the data is determined by said data comparing unit, outputs transfer information showing a position and a data length of the old file; a coincident portion search unit which, if a dissidence of the data is determined by said data comparing unit, searches the old file in both forward and backward directions from a data position where the dissidence has been determined on the old file, thereby searching a portion which coincides with the data of the new file; a shift information forming unit which, if the coincident portion can be searched by said coincident portion search unit, outputs shift information up to the coincident portion on the old file; and a replacement information forming unit which, if the coincident portion cannot be searched by said coincident portion search unit, adds new data to transfer replacement information showing a data length of the dissident portion of the old file at a position until the coincident portion can be searched and outputs resultant transfer replacement information. 